Signaling method and means therefor



May 17, 1932. w. VAN B. ROBERTS 1,858,810

SIGNALING METHOD AND MEANS THEREFOR Filed Oct. 4, 1928 RECTIFIER 4MP: mm12 INVENTOR AT ORNEY Patented May 17, 1932 r'rss PTENT F F 3 WALTER VANBRAAM ROBERTS, 0F PRINCETON, NEW JERSEY, ASSIGNOR TO RADIO C03IPORA'IION OF AMERICA, A COREOR-ATION OF DELAWARE SIGNALING METHODANDMEANS THEREFOR= Application filed 0ctober 4, 1928. Serial No. 310,240. 7

This invention relates to a method of signaling and means therefor, andmore par ticularly to a signaling system radiating a modulated radiofrequency wave.

During the reception of a broadcast signal it is often noticed that whena soft passage is received there is a great deal of hiss and noise.During the reception of a loud passage, this hiss and noise are drownedout. The first mentioned effect is due to the relative weakness of sidefrequencies caused by small percentage of modulation. The carrier, beingof constant amplitude, heterodynes stray noises as loudly during weakpassages as it does during loud ones.

This invention has, for one of its objects, the reduction of theseobjectionable noises during the reception of soft signals. This is doneby maintaining the average percentage of modulation approximatelyconstant for both soft and loud signals and simultaneously varying thestrength of all components of the radiated energy sothat at a receiverthe same effect as that of a constant amplitude carrier,'modulated by avariable amplitude signal, is obtained.

In the accompanying drawings which show ways of carrying out the mainobject of this invention, Figure 1' shows diagrammatically apparatus formaintaining the modulation of the output of an oscillator constant'andfor simultaneously varying the amount of energy radiated from theoscillator and Figure 2 showsapparatus for carrying out the functionsofthe apparatus of Figure 1 auto matically. 7

Referring to Figure 1, 1 indicates a microphone, 2 an audio frequencyamplifier, 3 a

modulator tube, 4 an oscillator, 5 a radio frequency amplifier, and 6 aradiating antenna. 'A leverage system 7, 8, 9 which may be actuatedmanually is provided for simultaneously varying the amplification ofthe.

audio frequency amplifier 2, for example, by

altering coupling or grid bias; and, the input to radio frequencyamplifier 5, for ex-' ample, by altering the coupling, to 5. q Avoltmeter V is placed in the output circuit of amplifier 2 to indicatethe voltage applied,

' quency'energy radiated. An additional amto the control electrode oftube 3. v v

The leverage system 7, 8, 9 should be arranged and manipulated so thatthe average output-voltage of amplifier 2 as indicated by V is keptsubstantially constant and so that thepower output of radio frequencypower amplifier 5 is varied in an inverse sens-e relative to the mannerin which the audio frequency signal 2 is amplified by amplifier 2.Adjustments ofthe control system which increase the amplification ofaudio amplifier 2 simultaneously decrease'the potentials applied to thepower amplifier 5, and vice versa. f

In this way, although the per cent of modulation of oscillator 4 remainsconstant,.the reversevariation of the power radiated causes the sameeffect to be obtained at a receiver as though ordinary variablemodulation of a constant: carrier were utilized, but with out the hisspresent when, the latter method of transmission is made use of.

The operation of the system shown in Figure '1 may be explainedmathematically as follows. Assume that the microphone out-. put voltageis E and the audio frequency 'amplification of amplifier 2 is A. Thenthe audio frequency input to modulator tube 3- is AE. If the frequencyof the audio current is F, then the modulated radio frequency 1y as(.1+KAE cos F) where K is a constant.

sion I-I cos Y (1+KAE'cos F) where H is proportional to the antennacurrent and Y is proportional to the carrier radio frequency.

' At the receiver the current of frequency F 'average'to' radiate agiven program'or signal.

Figure 2 shows apparatus for automatically varying the amplificationof'the audio frequency signals to be transmitted and for varying theamount; of modulated high frecurrent will vary in amplitudeapproximate-The radiated 'field is given by the expresplifier 10 is provided whichmay be connected across the input side of amplifier 2. The output ofamplifier 10 is fed into a rectifier 11. The direct current output ofrectifier 11 which will vary in accordance with the loudness of thesignals impressed 0n microphone l is fed through amplifier 12 intosolenoid 18. According to the strength of the input to microphone 1solenoid 13 magnetically draws on plunger 14; against the pull of'spring15 whose tension may be adjusted as found desirable. Levers 7 and 9 arethus automatically adjusted by intercallating elements 16, 17 fastenedto plunger 14 and link 8 respectively.

Members 16 and 17 are made to interfit so as to allow for the relativevertical movement of link 8 caused by the angular movement of links 7and -9. Lever 9 is caused to actuate the rotors of condenser 18 whosecapacity is varied in order to change the input to power amplifier 5.The plates on condenser 18 may be cut so that fora given amount of audioamplification by amplifier 2 a desired or predetermined amount ofmodulated radio fre quency energy is radiated.

It is to be noted that the system is designed to operate on averagechanges in amplitude of low frequency signals and'does not respond torapid changes such as a sudden high note or, when for example a shortburst of applause is radiated. Furthermore, if it is desired tobroadcast signals in the ordinary fashion, all that is necessary is, inFig. 1 to hold stationary the leverage system, and in Fig. 2, todisconnect the solenoid 13, for example, by disconnecting the input toamplifier 10.

Although the embodiments illustrated in the accompanying drawingsdisclose the principles of my invention and ways'in which they may becarried out successfully in practice, it will be apparent that variousminor changes will readily suggest themselves to those skilled in theart. Accordinglyuny inventi on is not to be limited by the modificationsshown but on the other hand is to be given the scope and breadthindicated in the appended claims.

l/Vhat I claim as my invention is:

1. The method of radiating a low frequency signal by modulating highfrequency energytherewith which includes varying the amplification ofthe low frequency signal so that the average percent of modulation ofthe high frequency energy shall remain substantially constant, andsimultaneously reactively varying the strength of the energy radiated ina manner opposite in sense relative to the manner in which theamplification of the low frequency signal is varied. 2. The method ofradiating low frequency "currents by modulating high frequency eny h ihw h ncludes automat a y varying the amplification of the low frequencycurrents so that by modulating the high frequency carrier energytherewith the average percent of modulation of the carrier energyremains substantially constant, and automatically reactively varying theamount of energy radiated in an opposite sense relative to the manner inwhich the amplification of the low frequency signal is varied.

3, The method of radiating a signal of varying amplitude which includesvariably amplifying the signals to a substantially constant averagevalue, modulating a carrier energy by the constant value amplifiedsignal and simultaneously reactively controlling in inverse sense to theamplification variation, the amount of carrier energy radiated.

4. In a radio signaling system means for amplifying a signal of variableamplitude to a substantially constant value, means for modulatingcarrier energy by the constant value amplified signal, and means forreactively controlling in inverse sense to the amplification, the amountof radiated carrier energy. a

5. In a radio signaling system means for amplifying in a predeterminedmanner a signal of variable amplitude, means for modulating carrierenergy by the amplified signal energy, and means for reactivelycontrolling in inverse manner relative to the amplification of themodulated carrier energy, the amount of modulated carrier energyradiated.

6. In combination, a source of signal energy, a source of carrierenergy, means for modulating carrier energy with the signal energy, anantenna, a variable reactance between the antenna and modulating meansto control the amount of carrier energy radiated, and means for varyingthe reactance inversely to the strength of the signal energy.

7. In a system for transmitting or conveying intelligence from onegeographically situated point to another geographically situated point,by means of propagated electromagnetic waves derived from the fiow ofundulatory electrical currents operated upon in accordance with theintelligence to be transmitted, an electron discharge device having anevacuated container wherein are contained an electron emitting cathode,an anode, and a grid interposed between the anode and cathode, means forsubjecting the electrodes within said container to high frequencyundulatory electrical potentials, an output circuit for said electrondischarge device, and, means for controlling the amount of highfrequency energy in said output circuit, said means comprising avariable condenser.

8. In an electrical system of the character described, the combinationof an electron discharge device having an anode, a cathode and a controlelectrode, each of said electrodes being subjected to high frequencypotentransmitting antenna system variably coupled to said modulator, anamplifier circuit having its input coupled to said source of signalfrequency and its output coupled to the input of a rectifying system andmeans coupled to the output of the rectifying system for controlling.the amount of signal energy fed from said source of signal frequency tosaid modulator and for varying the coupling between said antenna systemand said modulator.

10. In a Wireless transmission system in which a carrier frequency ismodulated by amplified signal energy, the method of reducing the effectof interference and at the same time maintaining the proper relationbetween the received signals and the signals desired to be transmittedwhich comprises variably amplifying the signal energy in a sense so asto maintain the voltage thereof approximately constant, modulating thecarrier frequency with the said approximately constant voltage signalenergy and variably transmitting the resulting energy said variationsbeing in opposite sense to the variations of amplification made uponsaid signal energy.

11. The method of transmitting signals by means of a carrier wave whichis modulated by amplified signals which comprises varyingsimultaneouslybut inopposite sense the amount of signal amplification and thetransmission gain of the entire modulated wave between the modulatingdevices and the radiator.

12. In a wireless transmission system in which a carrier frequency ismodulated by amplified signal energy, the method of reducing the efiectof interference and at the same time maintaining proper relationshipbetween signals desired to be transmitted and received signals whichcomprises variably amplifying the signal energy in a sense to maintainthe voltage thereof approximately constant, modulating the carrierfrequency energy with the approximately constant volt-age signal energyand varying the amountof the resulting modulated carrier frequencyenergy radiated into the ether simultaneously but in opposite sense tothe variations of amplification made upon said signal energy. V

13. In a wireless signaling system in which the carrier frequency ismodulated by signal energy, the combination with a modulator of a sourceof carrier frequency, a source ofsignal energy, both said sources beingoperatively connected to the modulator, said source of signal energybeing connected to said modulator through an amplifying circuit, meansin said amplifying circuit for varying the amount of amplification ofsaid signal energy, an antenna system variably coupled to saidmodulator, said coupling having means for controlling the amount ofmodulated carrier frequency energy allowed to pass from said modulatorto said'antenna system, a coupling device connected to both said meansand adapted to vary them simultaneously and in opposite sense;

WALTER VAN BRAAM ROBERTS.

